Field of the Invention
The invention relates to a method of positioning a roller that can be moved into at least two different operating positions in a printing machine. In addition, the invention relates to an inking unit for a printing machine having a roller that can be moved into at least two different operating positions.
Printing machines, and in particular rotary printing machines, of the generic type are already known. In an inking unit, it is usual for ink to be transmitted from a ductor roller to a vibrating roller and by means of the latter then to an ink distributor roller. To this end, the ductor roller is operatively connected in a manner known per se to an ink supply container to form a defined ink film on the ductor roller. In order to achieve metered transfer of ink, the vibrator roller is brought into operative contact with the ductor roller using an oscillatory movement (for example a swinging movement). The vibrator roller is subsequently moved from this first operating position into a second operating position, forming an operative contact between the latter and an ink distributor roller for the renewed transfer of ink. Known rolling mechanisms in rotary printing machines normally comprise still further intermediate and ink applicator rollers, by means of which ink is transferred, directly or indirectly, to a plate cylinder in order to ink a printing image located on the latter. This inked printing image is finally transferred onto the printing material to be printed using a blanket cylinder that is in frictional contact with the plate cylinder.
In order to oscillate the vibrator roller between the first operating position (operative contact between the vibrator roller and the ductor roller) and the second operating position (operative contact between the vibrator roller and the ink distributor roller), either a mechanical coupling between the vibrator roller and a main drive of the rotary printing machine, or a separate drive (Published German Patent Application DE 199 40 532 A1) is provided. For this purpose, known drive systems have a tilting lever and a cam disk which, when operated, displaces the longitudinal axis of the vibrator roller in the direction of the ductor roller or the ink distributor roller. In this case, the cam disk can either be coupled to the main drive of the rotary printing machine or can be provided with a separate drive motor.
Disadvantageously, in known rotary printing machines, undesired oscillations occur in the inking unit. Undesired oscillations are produced by the vibrator roller, or by the so-called vibrator shock, when the vibrator roller is moved in an oscillatory fashion between the ductor roller and the ink distributor roller. Vibrator shock is understood to mean the acceleration of the vibrator roller to the circumferential speed of the rapidly rotating ink distributor roller and the braking the vibrator roller to the circumferential speed of the slowly rotating ductor roller, which acceleration or braking is effected by friction between the circumferential surfaces of the vibrator roller and the ink distributor or ductor roller. These rotational oscillations, which in principle should be avoided, are transmitted to the plate cylinder, and therefore, also to the ink printing image on the blanket cylinder, and also to the web to be printed. As a result, unsatisfactory printing results are obtained.
It is accordingly an object of the invention to provide a method for positioning a roller and an inking unit which overcome the above-mentioned disadvantages of the prior art apparatus and methods of this general type.
In particular it is an object of the invention to provide a method for positioning a roller and an inking unit of the type previously mentioned in which oscillations that can be attributed to the oscillatory movement of a roller can be eliminated or at least reduced in the corresponding printing machine.
With the foregoing and other objects in view there is provided, in accordance with the invention, a method of positioning a roller that can be moved into at least two different operating positions in a printing machine, that includes steps of: mounting the roller in a magnetic bearing device; and positioning the roller into one of the at least two different operating positions by performing an operation selected from the group consisting of controlling the magnetic bearing device and regulating the magnetic bearing device.
A magnetic bearing device of this type permits the implementation of controlled-movement and freely predefinable positioning of the roller into a respective operating position. For example, in the case of a vibrator roller in an inking unit of a rotary printing machine, the production of an operative contact between the vibrator roller and the ductor roller (first operating position) and also between the vibrator roller and the ink distributor roller (second operating position) can be carried out gently and in a controlled manner such that undesired oscillations in the inking unit brought about on account of the vibrator shock are eliminated or at least reduced. It is possible, in a relatively simple and reliable manner, to ensure that the vibrator roller is placed against the ductor roller and, respectively, against the ink distributor roller virtually without oscillating. Furthermore, as a result using the magnetic bearing device, it is possible to adapt the revolution rate of the vibrator roller with respect to the main drive, so that the revolution rate, the contact time, and the pressing force of the vibrator roller can be controlled or regulated when a contacting connection is made with the ductor roller or the ink distributor roller. The main operating parameters (pressing force, contact time and revolution rate) for producing an operative contact between the vibrator roller and the ductor roller or the ink distributor roller, respectively, can therefore be predefined flexibly and can be matched precisely to the operating conditions of the printing machine that are present in each case and may vary over the course of time.
In accordance with an added feature of the invention, the positioning of the roller is carried out by means of an oscillatory movement in accordance with a predefinable movement profile. On the basis of predefinable, different movement profiles, the oscillatory movement of the roller may be determined freely and temporarily variably. Furthermore, in the case of a vibrator roller, the number of vibrator cycles in the rotary printing machine can be defined variably. In this case, by means of a free predefinition of the movement profile, it is possible to achieve a gentle and therefore oscillation-free or reduced-oscillation placement of the vibrator roller against the ductor roller or, respectively, the ink distributor roller. The movement profile can, for example, be chosen in such a way that the roller is moved rectilinearly or along a curve (same path for back and forth movement) or else along a closed, for example circular or elliptical, path (different part-sections for back and forth movement) in order to position the same in a respective operating position.
In accordance with an additional feature of the invention, in order to assume an operating position, the roller comes into a contact connection with a further roller such that a specific roller pressing force is established during the production of the contacting connection. The roller pressing force is predefinable by means of controlling or regulating the magnetic bearing device. A controllable or regulatable magnetic bearing device is particularly suitable for reliable and matched pressing force regulation when producing a contacting connection between two rollers. In this case, one can use the fact that actively regulated magnetic bearings belonging to the magnetic bearing device are suitable for executing a radial movement of a rotating body (roller), and at the same time, permit the setting of a resultant deflection force. On the basis of these relationships, a controlled and flexibly predefinable oscillatory movement of the roller can be implemented in an operationally beneficial manner.
In accordance with another feature of the invention, it is preferable for the oscillatory movement of the roller to be carried out in the form of a displacement that is substantially parallel to the longitudinal axis of the roller. An oscillatory movement of a roller of this type may be implemented in a relatively simple, precise and reliable manner by means of the controllable or regulatable magnetic bearing device.
In accordance with a further feature of the invention, the magnetic bearing device has two magnetic bearings arranged spaced apart from each other, by means of which the roller can be adjusted obliquely by applying electric current differently to the magnetic bearings. In addition, the possibility of alternative or additional oblique adjustment of the roller can be used as a further adjustable degree of freedom to eliminate or at least reduce undesired oscillations when producing a contacting connection between the roller (for example a vibrator roller) and a further roller (for example a ductor roller or ink distributor roller).
In accordance with a further added feature of the invention, according to a preferred design variant, measured values from position sensors and/or from an electric current that is applied to the magnetic bearing device are used in order to carry out roller bearing regulation. With the aid of position sensors, the distance established in each case between the rotor (roller) and the stator of the magnetic bearing device can be measured continuously, if appropriate.
As an alternative to position sensors, the respective position of the rotor (roller) can also be registered by determining the electric current applied to or impressed on the magnetic bearing device, and therefore the position can be controlled. A specific position sensor should preferably be provided for each mechanical degree of freedom of the roller. Position regulation taking account of the respective measured values from the position sensors and/or the electric current impressed on the magnetic bearing device ensures the gentle and oscillation-free or reduced-oscillation placement of the roller against a further roller.
Because the distance between the rotor and the stator of the magnetic bearing device is measured by means of a position sensor while the vibrator roller is resting on one of the rollers adjacent to it, and the resulting distance measurement signal is linked by computation in an electronic control device with the current consumption of the magnetic bearing device corresponding to this time, the degree of wear of the circumferential surface of the vibrator roller, of which the diameter decreases as a result of abrasive wear, can be monitored. The current consumption of the magnetic bearing device, which is proportional to the decrease in the diameter of the vibrator roller as a result of abrasive wear, therefore functions in measurement terms as a wear indicator. Of course, this presupposes that the position of that roller, for example the ductor roller, on which the vibrator roller rests during the measurement, and the distance of the position sensor from just this roller (ductor roller) are known.
In accordance with a further additional feature of the invention, the positioned roller can be a vibrator roller of an inking unit for a rotary printing machine, and the further roller can be a ductor roller or an ink distributor roller.
With the foregoing and other objects in view there is provided, in accordance with the invention, an inking unit for a printing machine that includes: a roller that can be moved into at least two different operating positions; and a magnetic bearing device mounting the roller. The magnetic bearing device is for positioning the roller into any of the operating positions. The magnetic bearing device is controlled or regulated in order to position the roller in a respective operating position.
In accordance with an added feature of the invention, the magnetic bearing device has two magnetic bearings, which are arranged spaced apart from each other and which can each be controlled or regulated independently. First, this ensures that the roller (vibrator roller) is reliably mounted, while at the same time ensures that the roller is precisely positioned, and if appropriate, enables the roller to be obliquely set.
In accordance with an additional feature of the invention, the magnetic bearings are advantageously operatively connected to an associated end of the roller. In this way, given an appropriate configuration of the ends of the roller, the formation of a relatively compact, symmetrically arranged magnetic bearing device, which is relatively easily accessible from the outside is made possible. In this case, the end of the roller can be formed, for example, as a reduced-cross-section journal, which is accommodated in an annular stator belonging to the associated magnetic bearing, forming a magnetic mounting.
In accordance with another feature of the invention, the magnetic bearing device is advantageously operatively connected to a control unit for regulating the position of the roller. By means of a suitable control unit, it is possible, in an operationally beneficial manner, to predefine a desired movement profile of the roller (vibrator roller) and to ensure correct positioning of the roller.
In accordance with a further feature of the invention, the control unit advantageously has at least one current sensor and/or at least one position sensor to regulate the position of the roller. In this case, the position sensors and the current sensors can be arranged to be integrated into the magnetic bearing device in a relatively compact manner and can be operatively connected to the control unit for the purpose of preferably continuous data transmission.
In accordance with a concomitant feature of the invention, the control unit has a specific position sensor for each mechanical degree of freedom of the roller. Since using a magnetic bearing device advantageously leads to a higher number of mechanical degrees of freedom of the roller (vibrator roller) as compared with the solutions from the prior art, a corresponding number of position sensors specific to the degrees of freedom should be provided in order to ensure correct and controlled positioning of the roller. Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in method of positioning a roller, which can be moved into at least two different operating positions in a printing machine, and corresponding inking unit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.